The present invention is directed toward a method for treating contact lenses and compositions for the same. The subject invention includes the use of an aqueous biguanide-containing disinfecting solution including an improved surfactant system comprising tyloxapol in combination with poloxamine for improving the stability of a polymeric biguanide disinfectant. Preferred embodiments of the invention include methods and compositions for simultaneously cleaning and disinfecting contact lenses.
Generally, contact lenses in wide use fall into three categories: (1) hard lenses formed from materials prepared by polymerization of acrylic esters, such as polymethyl methacrylate (PMMA), (2) rigid gas permeable (RGP) lenses formed from silicone acrylates and fluorosilicone methacrylates, and (3) gel, hydrogel or soft type lenses. The hard and rigid-type lenses, because they are characterized by low vapor diffusion and absorb only minor amounts of aqueous fluids, have a lower tendency to bind ingredients used in contact-lens care solutions. On the other hand, soft lenses have a greater tendency to bind active ingredients in contact-lens solutions and, therefore, it is especially challenging to develop solutions designed for the treatment of soft-type lenses, whether made from the more traditional copolymers of 2-hydroxyethylene methacrylate (HEMA) or from the newer silicon-containing hydrogel materials.
After wear, contact lenses must be disinfected to kill harmful microorganisms that may be present or grow on the lenses. Some of the most popular products for disinfecting lenses are multi-purpose solutions that can be used to clean, disinfect and wet contact lenses, followed by direct insertion (placement on the eye) without rinsing. Obviously, the ability to use a single solution for contact-lens care is an advantage. Such a solution, however, must be particularly gentle to the eye, since at least some of the solution will be on the lens when inserted and will come into contact with the eye.
U.S. Pat. No. 4,758,595 to Ogunbiyi et al. disclosed that a contact-lens solution containing a polyaminopropyl biguanide (PAPB), also known as polyhexamethylene biguanide (PHMB), has advantageous properties for a multi-purpose solution, especially in the presence of a borate buffer. These disinfecting and preservative solutions are especially noteworthy for their broad spectrum of bactericidal and fungicidal activity at low concentrations coupled with very low toxicity when used with soft-type contact lenses. Compositions containing PHMB and borate have been commercialized in various products including multi-purpose solutions, at relatively low levels of about 1 ppm or less, for use with soft contact lenses. U.S. Pat. Nos. 5,817,277; 5,593,637; and 5,422,073 to Mowrey-McKee et al. disclose a multi-purpose solution comprising a polyhexamethylene biguanide (PHMB) disinfectant in combination with the surfactants tyloxapol, poloxamine, or poloxamer for cleaning and disinfecting contact lenses.
A significant challenge to improving the cleaning efficacy of a multi-purpose solution is to simultaneously improve or maintain its disinfecting efficacy. The addition of more effective cleaning agents sometimes has the effect of reducing the efficacy of the disinfecting agent, in particular reducing the stability of the disinfecting agent over time. In particular, it is known that polymeric biguanides are not completely stable over time, hence requiring a limited shelf life when used at relatively low concentrations that are preferred for comfort reasons. Another challenge has been to develop a formula that is, on the one hand, maximally efficacious and, on the other hand, sufficiently gentle to be not only safe, but also comfortable for in-the-eye use.
One type of product that would require more efficacious cleaning and disinfection is a multi-purpose solution that would not require digital rubbing of the contact lens with the solution as part of its regimen of use. With conventional contact-lens cleaners or disinfectants, including multi-purpose solutions, lens wearers typically need to digitally or manually rub the contact lenses (typically between a finger and palm or between fingers) during treatment of the contact lenses. The necessity for the daily xe2x80x9crubbingxe2x80x9d of contact lenses adds to the time and effort involved in the daily care of contact lenses. Many contact-lens wearers dislike having to perform such a regimen or consider it to be inconvenient. Some wearers may be negligent in the proper xe2x80x9crubbingxe2x80x9d regimen, which may result in contact-lens discomfort and other problems. Sometimes rubbing, if performed too rigorously, which is particularly apt to occur with beginning lens wearers, may damage the lenses. This can be especially problematic when a replacement lens is not immediately available.
Contact lens solutions that qualify as a xe2x80x9cChemical Disinfecting Solutionxe2x80x9d do not require rubbing to meet biocidal performance criteria (for destroying representative bacteria and fungi) set by the US Food and Drug Administration (FDA) under the Premarket Notification (510 k) Guidance Document For Contact Lens Care Products, May 1, 1997. In contrast, a contact-lens solution, referred to as a xe2x80x9cChemical Disinfecting System,xe2x80x9d not qualifying as a Chemical Disinfecting Solution, requires a rubbing regimen to pass biocidal performance criteria. Traditionally, multi-purpose solutions (used for disinfecting and wetting or for disinfecting, cleaning, and wetting) have qualified as a Chemical Disinfecting System, but not as a Chemical Disinfecting Solution.
Traditional contact-lens multi-purpose solutions may depend on a rubbing regimen, not only for efficacious disinfection, but also for efficacious cleaning. Thus, in order to develop a contact-lens care solution that would not require rubbing, both improved or stronger cleaning and disinfection may be needed, while at the same time maintaining the solution sufficiently gentle for in-the-eye use.
Thus, it would be desirable to obtain a multi-purpose contact-lens solution that would provide increased disinfecting efficacy, particularly over time. Further, it would be desirable to obtain improved cleaning efficacy while maintaining or increasing the biocidal efficacy of the product without adversely affecting the comfort or safety in terms of the level of toxicity to eye tissue. While still more challenging to develop, it would also be desirable to develop a multi-purpose solution that exhibits both efficacious cleaning and disinfection of a contact lens, without requiring a rubbing regimen, or at least not inherently or invariably requiring it for acceptable performance, which multi-purpose solution allows direct placement of the contact lens on the eye following soaking of the lens in the solution and/or rinsing and rewetting the lens with the solution.
The present invention is directed to a biguanide-containing disinfecting solution containing tyloxapol in combination with a poloxamine for stabilizing polymeric biguanides, which is especially useful for contact-lens solutions that provide enhanced disinfecting and, in a preferred embodiment, both enhanced disinfecting and enhanced cleaning efficacy. The present invention includes methods for treating contact lenses and compositions used for the same. Specifically, the present invention involves contacting a contact lens with an aqueous solution having a pH of 5 to 8 and comprising:
(a) an effective amount of at least one polymeric biguanide germicide; and
(b) an effective amount of a poloxamine surfactant comprising at least about 90 weight percent of poly(oxyethylene) and poly(oxypropylene) segments, in one or more copolymer chains, wherein the weight average molecular weight of said surfactant is from about 10,000 to about 30,000 and wherein at least about 70 weight percent of said poly(oxyethylene) and poly(oxypropylene) segments are poly(oxyethylene) segments, and
(c) an effective amount of tyloxapol.
Preferably, the composition also comprises an effective amount of one or more sequestering agents. The method of the present invention comprises cleaning and disinfecting a contact lens with the above-described solution. In the preferred embodiment, products according to the present invention also provide enhanced cleaning while maintaining biocidal efficacy. In another embodiment of the present invention, the subject lens-care solution can both disinfect and clean a contact lens within a regimen not involving or requiring digital rubbing or the like. As such, the present invention offers significant advantages, including greater convenience and/or safety, compared to traditional cleaning and disinfecting solutions and methods of use.
The present invention can be used with all contact lenses such as conventional hard, soft, rigid and soft gas permeable, and silicone (including both hydrogel and non-hydrogel) lenses, but is especially useful for soft lenses. By the term xe2x80x9csoft lensxe2x80x9d is meant a lens having a proportion of hydrophilic repeat units such that the water content of the lens during use is at least 20% by weight. The term xe2x80x9csoft contact lensxe2x80x9d as used herein generally refers to those contact lenses that readily flex under small amounts of force. Typically, soft contact lenses are formulated from polymers having a certain proportion of repeat units derived from hydroxyethyl methacrylate and/or other hydrophilic monomers, typically crosslinked with a crosslinking agent. However, newer soft lenses, especially for extended wear, are being made from high-Dk silicone-containing materials.
The present invention is useful for contact-lens care solutions for simultaneously disinfecting and cleaning contact lenses, especially those that also qualify as a multi-purpose solution. In order to disinfect, the solution must contain one or more active ingredients (for example, anti-microbial agents and/or preservatives) in sufficient concentrations to destroy harmful microorganisms on the surface of a contact lens within the recommended minimum soaking time. The recommended minimum soaking time is included in the package instructions for use of the solution. The term xe2x80x9cdisinfecting solutionxe2x80x9d does not exclude the possibility that the solution may also be useful as a preserving solution, or that the disinfecting solution may be useful for other purposes such as daily cleaning, rinsing and storage of contact lenses, depending on the particular formulation.
A multi-purpose solution is useful for cleaning, disinfecting, storing, and rinsing a contact lens, particularly soft contact lenses. Multi-purpose solutions do not exclude the possibility that some wearers, for example, wearers particularly sensitive to chemical disinfectants or other chemical agents, may prefer to rinse or wet a contact lens with another solution, for example, a sterile saline solution prior to insertion of the lens. The term xe2x80x9cmulti-purpose solutionxe2x80x9d also does not exclude the possibility of periodic cleaners not used on a daily basis or supplemental cleaners for removing proteins, for example enzyme cleaners, which are typically used on a weekly basis. By the term xe2x80x9ccleaningxe2x80x9d is meant that the solution contains one or more cleaning agents in sufficient concentrations to loosen and remove loosely held lens deposits and other contaminants on the surface of a contact lens, which may be used in conjunction with digital manipulation (for example, manual rubbing of the lens with a solution) or with an accessory device that agitates the solution in contact with the lens, for example, a mechanical cleaning aid. The critical micelle concentration of a surfactant-containing solution is one way to evaluate its cleaning effectiveness.
Traditionally, multi-purpose solutions on the market have required a regimen involving mechanical rubbing of the contact lens with the multi-purpose solution, in order to provide the required disinfection and cleaning. Such a regimen is required under governmental regulatory authorities (for example, the FDA or Food and Drug Administration in the USA) for a Chemical Disinfection System that does not qualify as a Chemical Disinfecting Solution. In one embodiment of the present invention, it is possible to formulate a cleaning and disinfecting product that, on the one hand, is gentle enough to be used as a wetting agent and, on the other hand, is able to provide improved cleaning and disinfection in the absence of a rubbing regimen. For example, a product qualifying as a Chemical Disinfecting Solution must meet biocidal performance criteria established by the US FDA for Contact Lens Care Products (May 1, 1997) which criteria does not involve rubbing of the lenses. In one embodiment of the present invention, a composition is formulated to meet the requirements of the FDA or ISO Stand-Alone Procedure for contact lens disinfecting products. Similarly, compositions of the present invention can be formulated to provide enhanced cleaning without the use of a rubbing regimen. Such formulations may ensure higher patient compliance and greater universal appeal than traditional multi-purpose disinfecting and cleaning products.
The solutions according to the present invention are physiologically compatible. Specifically, the solution must be xe2x80x9cophthalmically safexe2x80x9d for use with a contact lens, meaning that a contact lens treated with the solution is generally suitable and safe for direct placement on the eye without rinsing, that is, the solution is safe and comfortable for daily contact with the eye via a contact lens that has been wetted with the solution. An ophthalmically safe solution has a tonicity and pH that is compatible with the eye and comprises materials, and amounts thereof, that are non-cytotoxic according to ISO (International Standards Organization) standards and U.S. FDA (Food and Drug Administration) regulations. The solution should be sterile in that the absence of microbial contaminants in the product prior to release must be statistically demonstrated to the degree necessary for such products.
The subject solution includes at least one polymeric biguanide antimicrobial agent. A polymeric biguanide can optionally be combined with a non-polymeric biguanide. Representative non-polymeric biguanides are the bis(biguanides), such as alexidine or chlorhexidine or salts thereof. Representative polymeric biguanides include hexamethylene biguanide (PHMB). Preferred polymeric biguanides, and water-soluble salts thereof, have the following formula: 
wherein Z is an organic divalent bridging group which may be the same or different throughout the polymer, n is on average at least 3, preferably on average 5 to 20, and X1 and X2 are independently selected from the groups xe2x80x94NH2 and 
One preferred group of water-soluble polymeric biguanides will have number average molecular weights of at least 1,000 and more preferably will have number average molecular weights from 1,000 to 50,000. Suitable water-soluble salts of the free bases include, but are not limited to hydrochloride, borate, acetate, gluconate, sulfonate, tartrate and citrate salts.
The above-disclosed biguanides and methods of preparation are described in the literature. For example, U.S. Pat. No. 3,428,576 describes the preparation of polymeric biguanides from a diamine and salts thereof and a diamine salt of dicyanimide.
Most preferred are the polymeric hexamethylene biguanides, commercially available, for example, as the hydrochloride salt from Zeneca (Wilmington, Del.) under the trademark Cosmocil(trademark) CQ. Such polymers and water-soluble salts are referred to polyhexamethylene biguanide (PHMB) or polyaminopropyl biguanide (PAPB). The term polyhexamethylene biguanide, as used herein, is meant to encompass one or more biguanides have the following formula: 
wherein X1 and X2 are as defined above and n is from 1 to 500.
Depending on the manner in which the biguanides are prepared, the predominant compound falling within the above formula may have different X1 and X2 groups or the same groups, with lesser amounts of other compounds within the formula. Such compounds are known and are disclosed in U.S. Pat. No. 4,758,595 and British Patent 1,432,345, which patents are hereby incorporated herein by reference. Preferably, the water-soluble salts are compounds where n has an average value of 2 to 15, most preferably 3 to 12.
A disinfecting amount of antimicrobial agent is an amount that will at least partially reduce the microorganism population in the formulations employed. Preferably, a disinfecting amount is that which will reduce the microbial burden of representative bacteria by two log orders in four hours and more preferably by one log order in one hour. Most preferably, a disinfecting amount is an amount which will eliminate the microbial burden on a contact lens when used according to its regimen for the recommended soaking time (FDA Chemical Disinfection Efficacy Test - July 1985 Contact Lens Solution Draft Guidelines). Typically, such agents are present in concentrations ranging from about 0.00001 to about 0.5% (w/v), and more preferably, from about 0.00003 to about 0.5% (w/v).
In one preferred embodiment, a polymeric biguanide is used in combination with a bis(biguanide) compound. Polymeric biguanides, in combination with bis(biguanide)s such as alexidine, are effective in concentrations as low as 0.00001 weight percent (0.1 ppm). It has also been found that the bactericidal activity of the solutions may be enhanced or the spectrum of activity broadened through the use of a combination of such polymeric biguanides with alexidine or similar biguanide, as disclosed in commonly assigned copending U.S. application Ser. No. 09/190,899, filed Nov. 12, 1998, hereby incorporated by reference.
An optional non-biguanide disinfectant/germicide can be employed as a solution preservative, but it may also function to potentiate, complement or broaden the spectrum of microbiocidal activity of another germicide. This includes microbiocidally effective amounts of germicides which are compatible with and do not precipitate in the solution, in concentrations ranging from about 0.00001 to about 0.5 weight percent, and more preferably, from about 0.0001 to about 0.1 weight percent. Suitable complementary germicidal agents include, but are not limited to, quaternary ammonium polymers, sorbic acid, alkyl triethanolamines, and mixtures thereof. Representative examples of the polymeric quaternary ammonium salts used in ophthalmic applications are poly[(dimethyliminio)-2-butene-1,4-diyl chloride], [4-tris(2-hydroxyethyl)ammonio]-2-butenyl-w-[tris(2-hydroxyethyl)ammonio]dichloride (chemical registry number 75345-27-6) generally available as polyquaternium 1 (copyright) from ONYX Corporation. Novel Polyquaterniums are disclosed in copending U.S. application Ser. No. 60/065,510 filed Nov. 12, 1997, hereby incorporated by reference.
The acid-addition salts of the germicides used in the present composition may be derived from an inorganic or organic acid. In most circumstances it is preferable that the salts be derived from an acid which is readily water soluble and which affords an anion that is suitable for human usage, for example a pharmaceutically-acceptable anion. Examples of such acids are hydrochloric, hydrobromic, phosphoric, sulphuric, acetic, D-gluconic, 2-pyrrolidino-5-carboxylic, methanesulphonic, carbonic, lactic and glutamic acids. The hydrochloride salt is preferred.
As indicated above, the present solution comprises at least one poloxamine surfactant that has known advantages in terms of cleaning efficacy and comfort. See, for example, U.S. Pat. No. 4,820,352 to Riedhammer and copending, U.S. application Ser. No. 09/211,547, filed Dec. 15, 1998, hereby incorporated by reference. In general, poloxamine surfactants comprise a poly(oxypropylene)-poly(oxyethylene) adduct of ethylene diamine. The surfactant should be soluble in the lens care solution, not become turbid, and should be non-irritating to eye tissues. Preferred poloxamines comprise at least about 90 weight percent of poly(oxyethylene) and poly(oxypropylene) segments in one or more block copolymer chains, wherein the weight average molecular weight of said surfactant is from about 4000 to about 30,000 and wherein at least about 70 percent of said segments are poly(oxyethylene) segments. Such surfactants are available from BASF Wyandotte Corp., Wyandotte, Mich., under the registered trademark xe2x80x9cTetronic.xe2x80x9d Poloxamine is the CTFA Cosmetic Ingredient Dictionary""s adopted name for this group of surfactants. Such surfactants are commercially available from BASF Wyandotte Corp., Wyandotte, Mich., under the registered trademark xe2x80x9cTetronic.xe2x80x9d Examples of preferred poloxamines include Tetronic(copyright) 707, Tetronic(copyright) 908, Tetronic(copyright) 909, Tetronic(copyright) 1508, Tetronic(copyright) 1107 and combinations thereof.
It has been found that the addition of another conventional surfactant to the poloxamine, namely tyloxapol, improves the stability, and hence disinfecting efficacy over time, of biguanides in the solution, particularly solutions with enhanced cleaning and disinfection. Tyloxapol is an oxyethylated tertiary octylphenol formaldehyde polymer. Its preparation is disclosed in U.S. Pat. No. 2,454,541 to Bock and Rainey. It is commercially available from Rohm and Haas Co.(Philadelphia, Pa.). As indicated by its known chemical structure, tyloxapol is a nonionic surfactant with surface tension reducing properties that is freely soluble in water.
The poloxamine and the tyloxapol are each suitably employed in amounts ranging from 0.01 to 10.0 percent, preferably 0.1 to 5.0 percent, most preferably 0.5 to 1.5 percent by weight of the composition or solution.
Additional optional surfactants can be either amphoteric, cationic, anionic, or nonionic which may be present (individually or in combination) in amounts up to 10 percent, preferably up to 5 percent weight by volume (w/v) of the total composition (solution). Preferably, any additional surfactants are amphoteric or nonionic surfactants, which when used impart cleaning and conditioning properties. The surfactant should be soluble in the lens care solution and non-irritating to eye tissues. Optionally additional non-ionic surfactants include polyethylene glycol esters of fatty acids, e.g. coconut, polysorbate, polyoxyethylene or polyoxypropylene ethers of higher alkanes (C12-C18). Examples include polysorbate 20 (available under the trademark Tween(copyright) 20), polyoxyethylene (23) lauryl ether (Brij(copyright) 35), polyoxyethyene (40) stearate (Myrj(copyright) 52), polyoxyethylene (25) propylene glycol stearate (Atlas(copyright) 2612).
Amphoteric surfactants suitable for use in a composition according to the present invention include materials of the type are offered commercially under the trade name xe2x80x9cMiranol.xe2x80x9d Another useful class of amphoteric surfactants is exemplified by cocoamidopropyl betaine, commercially available from various sources.
Various other surfactants suitable for use in the composition can be readily ascertained, in view of the foregoing description, from McCutcheon""s Detergents and Emulsifiers, North American Edition, McCutcheon Division, MC Publishing Co., Glen Rock, N.J. 07452 and the CTFA International Cosmetic Ingredient Handbook, Published by The Cosmetic, Toiletry, and Fragrance Association, Washington, D.C.
As indicated above, the concentration of the surfactants, including the required poloxamine in combination with the required tyloxapol and any additional conventional surfactactants, is suitably in total from 0.01 to 10.0 percent weight by volume (w/v), preferably 0.1 to 5.0 percent, and most preferably 0.5 to 1.5 percent.
In one preferred embodiment, it has been found that the cleaning efficacy of the solution can be enhanced by including a carbonate or bicarbonate salt in the amount of 0.010 to 1.0 percent by weight of the total composition (solution), preferably 0.05 to 0.2 weight percent, most preferably 0.08 to 0.12 weight percent. Suitably, the carbonate or bicarbonate salt is an alkali metal salt, including, for example, sodium bicarbonate, sodium carbonate, potassium carbonate, potassium bicarbonate, and mixtures thereof. The most preferred carbonates are sodium carbonate and sodium bicarbonate.
It may also be desirable to include water-soluble viscosity builders in the solutions of the present invention. Because of their demulcent effect, viscosity builders have a tendency to enhance the lens wearer""s comfort by means of a film on the lens surface cushioning impact against the eye. Included among the water-soluble viscosity builders are the cellulose polymers like hydroxyethyl or hydroxypropyl cellulose, carboxymethyl cellulose, povidone, polyvinyl alcohol, and the like. Such viscosity builders may be employed in amounts ranging from about 0.01 to about 4.0 weight percent or less.
In the present application, the amount of the germicide or other components or ingredients in a solution according to the present invention refers to the amount formulated and introduced into the solution at the time the solution is made.
In addition to a biguanide germicide and the stabilizing amount of a poloxamine, the solutions of the present invention include a buffering system. In a preferred embodiment, the buffer system includes at least one phosphate buffer and at least one borate buffer, which buffering system has a buffering capacity of 0.01 to 0.5 mM, preferably 0.03 to 0.45, of 0.01 N of HCl and 0.01 to 0.3, preferably 0.025 to 0.25, of 0.01 N of NaOH to change the pH one unit. Buffering capacity is measured by a solution of the buffers only.
The pH of the present solutions should be maintained within the range of 5.0 to 8.0, more preferably about 6.0 to 8.0, most preferably about 6.5 to 7.8. By the terms xe2x80x9cbufferxe2x80x9d or xe2x80x9cbuffer substancexe2x80x9d is meant a compound that, usually in combination with at least one other compound, provides a buffering system in solution that exhibits buffering capacity, that is, the capacity to neutralize, within limits, either acids or bases (alkali) with relatively little or no change in the original pH. The term xe2x80x9cbuffering capacityxe2x80x9d is defined to mean the millimoles (mM) of strong acid or base (or respectively, hydrogen or hydroxide ions) required to change the pH by one unit when added to one liter (a standard unit) of the buffer solution. From this definition, it is apparent that the smaller the pH change in a solution caused by the addition of a specified quantity of acid or alkali, the greater the buffer capacity of the solution. See, for example, Remington: The Science and Practice of Pharmacy, Mack Publishing Co., Easton, Pa. (19th Edition 1995), Chapter 17, pages 225-227. The buffer capacity will depend on the kind and concentration of the buffer components. The buffer capacity is measured from a starting pH of 6 to 8, preferably from 7.4 to 8.4.
Borate buffers include, for example, boric acid and its salts, for example, sodium borate or potassium borate. Borate buffers also include compounds such as potassium tetraborate or potassium metaborate that produce borate acid or its salt in solutions. Phosphate buffers include, for example, phosphoric acid and its salts, for example, phosphate buffers (including combinations of M2HPO4, MH2PO4 and MH2PO4, wherein M is independently an alkali metal salt such as K and Na). The term phosphate includes compounds that produces phosphoric acid or its salt in solution. As will be readily appreciated by the skilled artisan, buffering systems include but are not limited to the combination of a weak acid and the salt of the weak acid (the so-called conjugate base).
An especially preferred buffer system is the combination of boric acid and mono and/or dibasic phosphate salt such as sodium and/or disodium phosphate. An alternate buffer system, for example, are the combination of sodium borate and phosphoric acid or the combination of sodium borate and the monobasic phosphate.
Suitably the solution comprises about 0.05 to 2.5% by weight of a phosphoric acid or its salt and 0.1 to 5.0% by weight of boric acid or its salt. The phosphate buffer is used (in total) at a concentration of 0.004 to 0.2 M (Molar), preferably 0.04 to 0.1 M. The borate buffer (in total) is used at a concentration of 0.02 to 0.8 M, preferably 0.07 to 0.2 M.
Other buffer substances may optionally be used in the composition. For example, traditionally known buffers include, for example, citrates, citric acid, sodium bicarbonate, TRIS, and the like. Generally, buffers will be used in amounts ranging from about 0.05 to 2.5 percent by weight, and preferably, from 0.1 to 1.5 percent.
Borate buffers are known for enhancing the efficacy of certain polymeric biguanides. For example, U.S. Pat. No. 4,758,595 to Ogunbiyi et al. discloses that a contact-lens solution containing a polyaminopropyl biguanide (PAPB), also known as polyhexamethylene biguanide (PHMB), has enhanced efficacy when combined with a borate buffer. Applicants have found that borate buffers also enhance the efficacy of biguanides in general, including bis(biguanides) such as alexidine.
In addition to buffering agents, in some instances it may be desirable to include sequestering agents in the present solutions in order to bind metal ions that might otherwise react with the lens and/or protein deposits and collect on the lens. They are usually added in amounts ranging from about 0.01 to about 0.2 weight percent. Examples include Ethylene-diaminetetraacetic acid (EDTA) and its salts (disodium), gluconic acid, citric acid, tartaric acid and their salts, e.g. sodium salts. Preferred sequestering agents, which are also effective for removing protein deposits, are the phosphonate compounds represented by the following Formula (I): 
wherein Z is a connecting radical equal in valence to n, wherein n is an integer from 1 to 6, preferably 1 to 3. Such phosphonate compounds are disclosed in WO 97/31659. The subject aqueous solution suitably includes at least 0.003 percent weight by volume of the subject phosphonic compound in the total solution, preferably 0.005 to 2.5 percent weight by volume and more preferably about 0.01 to 0.5 percent weight by volume in the total solution.
Typically, the aqueous solutions of the present invention for treating contact lenses are also adjusted with tonicity agents, to approximate the osmotic pressure of normal lachrymal fluids which is equivalent to a 0.9 percent solution of sodium chloride or 2.5 percent of glycerol solution. The solutions are made substantially isotonic with physiological saline used alone or in combination, otherwise if simply blended with sterile water and made hypotonic or made hypertonic the lenses will lose their desirable optical parameters. Correspondingly, excess saline may result in the formation of a hypertonic solution that will cause stinging and eye irritation. Examples of suitable tonicity adjusting agents include, but are not limited to: sodium and potassium chloride, dextrose, glycerin, calcium and magnesium chloride. These agents are typically used individually in amounts ranging from about 0.01 to 2.5 % (w/v) and preferably, form about 0.2 to about 1.5% (w/v). Preferably, the tonicity agent will be employed in an amount to provide a final osmotic value of 200 to 450 mOsm/kg and more preferably between about 250 to about 350 mOsm/kg, and most preferably between about 280 to about 320 mOsm/Kg.
Preferably, the invention is formulated as a xe2x80x9cmulti-purpose solution,xe2x80x9d meaning that the solution may be used for cleaning, chemical disinfection, storing, and rinsing a contact lens. A multi-purpose solution preferably has a viscosity of less than 75 cps, preferably 1 to 50 cps, and most preferably 1 to 25 cps and is preferably is at least 95 percent weight by volume water in the total composition.
As stated above, contact lenses are cleaned and disinfected by contacting the lens with the subject aqueous solution. Although this may be accomplished by simply soaking a lens in the subject solution, greater cleaning can be achieved if a few drops of the solution are initially placed on each side of the lens, and the lens is rubbed for a period of time, for example, approximately 20 seconds. The lens can then be subsequently immersed within several milliliters of the subject solution. Preferably, the lens is permitted to soak in the solution for at least four hours. Furthermore, the lens is preferably rinsed with fresh solution after any rubbing step and again after being immersed within the solution. The lenses are then removed from the solution, rinsed with the same or a different solution, for example a preserved isotonic saline solution and then replaced on the eye.
The aqueous solutions of the present invention are especially useful for soft contact lenses, with or without further additives. Nevertheless, the solutions of the present invention may be formulated into specific contact lens care products, such as wetting solutions, soaking solutions, cleaning and conditioning solutions, as well as multi-purpose type lens care solutions, etc. and mixtures thereof. Finally, such solutions can be applied to the lenses outside the eye or while on the eye, for example, in the form of droplets.
As indicated above, contact-lens wearers are commonly required to digitally or manually rub the contact lenses (typically between a finger and palm or between fingers) during daily cleaning and/or disinfecting of contact lenses. In one embodiment of the present invention, a method is provided in which rubbing is not required during treatment with the claimed specified solution, between removal from the eye and replacement of the lens following lens care. In a preferred embodiment of such a method, a soft lens is disinfected or both disinfected and cleaned with a multi-purpose solution or an effective multi-purpose solution that is the only daily solution needed for treating the lens outside the eye. Thus, in one embodiment of a method according to the invention, the described solution is used to treat a contact lens without rubbing, by a method comprising:
(a) soaking the contact lens that has not been rubbed with the solution for a specified time period, and
(b) direct placement of the treated contact lens on the eye of the wearer.
Typically, step (a) may involve immersing the contact lens in the solution. Soaking may optionally comprise shaking or similarly agitating a container of the solution by manual means. Preferably, step (a) involves a period of soaking the contact lens in a container wherein the contact lens is completely immersed in the solution. By the term xe2x80x9cdirect placementxe2x80x9d is herein meant that the solution is not diluted or rinsed off the lens with a different contact-lens solution prior to xe2x80x9cinsertionxe2x80x9d or placement on the eye. In a particularly preferred embodiment, the method uses a product that is formulated as a multi-purpose, wherein no other solution or product is required for daily cleaning of the lens, with the possible exception of an enzyme cleaner.
In yet another embodiment of a method according to the present invention, the claimed solution is used to clean a frequent replacement lens (FRL) or planned replacement lens (PRL) that is planned for replacement after not more than about three months of use in the eye, or that is planned for replacement after not more than about 30 days of use in the eye, or that is planned for replacement after not more than about two weeks in the eye. Preferably, the lens is made from a polymer comprising about 0.0 to 5 mole percent repeat units derived from methacrylic acid (MAA), 10 to 99 mole percent of repeat units derived from hydroxyethyl methacrylate, and about 0.5 to 5 mole percent of cross-linking repeat units. Cross-linking repeat units may be derived, for example, from such monomers as ethyleneglycol dimethacrylate, divinylbenzene, and trimethylpropane trimethacrylate.